High energy materials for a battery and methods for making and use

ABSTRACT

A method of forming an electrode active material by reacting a metal fluoride and a reactant. The method includes a coating step and a comparatively low temperature annealing step. Also included is the electrode formed following the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of International ApplicationNo. PCT/US2014/028506, having an international filing date of Mar. 14,2014 entitled “High Energy Materials For A Battery And Methods ForMaking And Use,” which claims priority to U.S. Provisional ApplicationNo. 61/786,602 filed Mar. 15, 2013 entitled “High Energy Materials For ABattery And Methods For Making And Use.” This application claimspriority to and the benefit of each of these applications, and eachapplication is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention is in the field of battery technology, and moreparticularly in the area of materials for making high-energy electrodesfor batteries, including metal-fluoride materials.

One type of battery consists of a negative electrode made primarily fromlithium and a positive electrode made primarily from a compoundcontaining a metal and fluorine. During discharge, lithium ions andelectrons are generated from oxidation of the negative electrode whilefluoride ions are produced from reduction of the positive electrode. Thegenerated fluoride ions react with lithium ions near the positiveelectrode to produce a compound containing lithium and fluorine, whichmay deposit at the positive electrode surface.

Metal fluoride based batteries are an attractive energy storagetechnology because of their extremely high theoretical energy densities.For example, certain metal fluoride active materials can havetheoretical energy densities greater than about 1600 Wh/kg or greaterthan about 7500 Wh/L. Further, metal fluorides have a relatively low rawmaterial cost, for example less than about $10/kg. However, a number oftechnical challenges currently limit their widespread use andrealization of their performance potential.

One challenge for certain metal fluoride materials is comparatively poorrate performance. Many metal fluoride active materials haveelectrochemical potentials greater than about 2.5 V because of theirrelatively large bandgap produced by the highly ionic bonding betweenthe metal and fluorine, and in particular between a transition metal andfluorine. Unfortunately, one of the drawbacks to wide bandgap materialsis the intrinsically low electronic conductivity that results from thewide bandgap. As a result of this low conductivity, discharge rates ofless than 0.1 C are required in order to obtain full theoreticalcapacity. More typically, discharge rates of 0.05 C to 0.02 C arereported in the literature. Such low discharge rates limit thewidespread use of metal fluoride active materials.

Another challenge for certain metal fluoride active materials is asignificant hysteresis observed between the charge and dischargevoltages during cycling. This hysteresis is typically on the order ofabout 1.0V to about 1.5V. While the origin of this hysteresis isuncertain, current evidence suggests that kinetic limitations imposed bylow conductivity play an important role. Further, asymmetry in thereaction paths upon charge and discharge may also play a role. Since theelectrochemical potential for many of the metal fluorides is on theorder of 3.0V, this hysteresis of about 1.0V to about 1.5V limits theoverall energy efficiency to approximately 50%.

Limited cycle life is another challenge for certain metal fluorideactive materials. Although rechargeability has been demonstrated formany metal fluoride active materials, their cycle life is typicallylimited to tens of cycles and is also subject to rapid capacity fade.Two mechanisms are currently believed to limit the cycle life for themetal fluoride active materials: agglomeration of metallic nanoparticlesand mechanical stress due to volume expansion. It is believed that metalfluoride active materials can cycle by virtue of the formation duringlithiation of a continuous metallic network within a matrix ofinsulating LiF. As the number of cycles increases, the metal particlestend to accumulate together into larger, discrete particles. The largeragglomerated particles in turn create islands that are electricallydisconnected from one another, thus reducing the capacity and ability tocycle the metal fluoride active materials. The second limitation toextended cycle life is the mechanical stress imparted to the bindermaterials by the metal fluoride particles as a result of the volumeexpansion that occurs during the conversion reaction. Over time, thebinder is pulverized, compromising the integrity of the cathode.Notably, for the metal fluoride CuF₂, no demonstrations ofrechargeability have been reported.

For CuF₂, an additional challenge prevents rechargeability. Thepotential required to recharge a CuF₂ electrode is 3.55V. However, intypical electrolytes for lithium ion batteries, Cu metal oxidizes toCu²⁺ at approximately 3.4 V vs. Li/Li⁺. The oxidized copper can migrateto the anode, where it is irreversibly reduced back to Cu metal. As aresult, Cu dissolution competes with the recharge of Cu+2LiF to CuF₂,preventing cycling of the cell. The Cu metal accumulating on the anodesurface can increase the impedance and/or destroy the solid-electrolyteinterphase (SEI) on the anode.

The following papers and patents are among the published literature onmetal fluorides that employ mixed conductors that are notelectrochemically active within the voltage window of the metalfluoride: Badway, F. et al., Chem. Mater., 2007, 19, 4129; Badway, F. etal., J. Electrochem. Soc., 2007, 150, A1318; “Bismuth fluoride basednanocomposites as electrode materials” U.S. Pat. No. 7,947,392; “MetalFluoride And Phosphate Nanocomposites As Electrode Materials” US2008/0199772; “Copper fluoride based nanocomposites as electrodematerials” US 2006/0019163; and “Bismuth oxyfluoride basednanocomposites as electrode materials” U.S. Pat. No. 8,039,149.

Certain embodiments of the present invention can be used to formelectrochemical cells having metal fluoride active material that exhibitimproved rate performance, improved energy efficiency, and improvedcycle life when compared to prior batteries. Thus, these and otherchallenges can be addressed by embodiments of the present inventiondescribed below.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the invention include a method of making acomposition for use in forming a cathode for a battery. The methodincludes coating a metal fluoride material with a coating precursormaterial including a metal or a metal complex and annealing coated metalfluoride material, wherein at least a portion of the metal fluoridematerial and at least a portion of the coating undergo a phase change.The metal fluoride material is preferably CuF₂. The metal can be, forexample, Ni, Ba, or Ta. The metal complex can be, for example a metaloxide, such as A₁₂O₃, SiO₂, Ta₂O₅, TiO₂; a metal nitride, such as AlN,TaN; a metal silicate, such as ZrSiO₄; or other materials that arevolatile enough to be evaporated and re-condensed onto a substrate. Theannealing temperature is less than 450 degrees C, less than 400 degreesC, less than 325 degrees C, or less than 200 degrees C. Preferably, theannealing temperature is about 325 degrees C. The temperature is chosensuch that it is sufficiently high for the metal complex to react withthe metal fluoride, but not high enough to decompose the metal fluoride.Without such heat treatment and the resulting reaction, the material isnot rechargeable, as is demonstrated by experiments described herein.

Certain embodiments of the invention include a composition formed by themethods disclosed herein. The composition is characterized by havingreversible capacity. The composition can include particles with a grainsize greater than 100 nm, 110 nm, 120 nm, or 130 nm. The composition caninclude a particle having a first phase and a coating on the particlehaving a second phase. Preferably, the first phase includes the metalfluoride and the second phase includes the metal oxide. The coating canbe covalently bonded to the particle.

Certain embodiments of the invention include batteries having electrodesformed from the compositions disclosed herein, the method of making suchbatteries, and the method of use of such batteries.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates electrochemical characterization of different hybridcathode formulations according to embodiments of the invention in whichthe content of a conductive precursor material is varied in the cathode.

FIG. 2 illustrates electrochemical characterization of a cathodeformulation from FIG. 1 in which the voltage of a hybrid cathodeaccording to embodiments of the invention is plotted against thecapacity for the first and second cycles.

FIG. 3 illustrates electrochemical characterization of different hybridcathode formulations according to embodiments of the invention in whichthe discharge is plotted as a function of cycle for 10 cycles.

FIG. 4 illustrates electrochemical characterization of a hybrid cathodeformed from a metal fluoride and a reactant material according tocertain embodiments. The cathode demonstrates rechargeability.

FIG. 5 illustrates a powder X-ray diffraction pattern of a material usedto form a rechargeable metal fluoride cathode.

FIG. 6 illustrates second cycle discharge capacity for a variety ofhybrid cathode materials used according to embodiments of the invention.

FIG. 7 illustrates second cycle discharge capacity for a hybrid cathodematerial used according to embodiments of the invention versus annealingtemperature.

FIG. 8 illustrates second cycle the capacity retention and reversiblecapacity for cathode active materials formed from reacting 85 wt % CuF₂with 15 wt % of certain metal oxides (in this case NiO or TiO₂) atcertain annealing temperatures.

FIG. 9 illustrates the second-cycle capacity retention and reversiblecapacity for cathode active materials formed from reacting 85 wt % CuF₂with 15 wt % of certain metal oxides (in this case NiO or TiO₂) forcertain annealing times.

FIG. 10 illustrates the second-cycle capacity retention and reversiblecapacity for cathode active materials formed from reacting 85 wt %, 90wt %, or 95 wt % CuF₂ with 5 wt %, 10 wt %, 15 wt % of NiO.

FIG. 11 illustrates the second-cycle capacity retention and reversiblecapacity for cathode active materials formed from reacting 85 wt %, CuF₂with 15 wt % of NiO as a function of milling energy.

FIG. 12 illustrates the second-cycle capacity retention and reversiblecapacity for cathode active materials formed from reacting 85 wt %, CuF₂with 15 wt % of NiO as a function of milling time.

FIG. 13 illustrates the second cycle reversible capacity measured forvarious starting materials used to react with CuF₂.

FIG. 14 illustrates the second-cycle capacity retention and reversiblecapacity for cathode active materials formed from reacting CuF₂ withnickel(II) acetylacetonate using various processing conditions.

FIG. 15 illustrates the capacity as a function of cycle for cathodeactive materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiOand for a control material.

FIG. 16 illustrates a galvanostatic intermittent titration techniquemeasurement for cathode active materials formed from reacting 85 wt %,CuF₂ with 15 wt % of NiO.

FIG. 17 illustrates the capacity of full cells and half cells as afunction of cycle for cathode active materials formed from reacting 85wt %, CuF₂ with 15 wt % of NiO.

FIG. 18 illustrates voltage traces of the full cell and half cellsprepared as described in relation to FIG. 17.

FIG. 19 illustrates the capacity retention of full cells and half cellsas a function of cycle for cathode active materials formed from reacting85 wt %, CuF₂ with 15 wt % of NiO.

FIG. 20 illustrates the second cycle reversible capacity measured forvarious coating precursor materials used to react with CuF₂.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions apply to some of the aspects described withrespect to some embodiments of the invention. These definitions maylikewise be expanded upon herein. Each term is further explained andexemplified throughout the description, figures, and examples. Anyinterpretation of the terms in this description should take into accountthe full description, figures, and examples presented herein.

The singular terms “a,” “an,” and “the” include the plural unless thecontext clearly dictates otherwise. Thus, for example, reference to anobject can include multiple objects unless the context clearly dictatesotherwise.

The terms “substantially” and “substantial” refer to a considerabledegree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels or variability of the embodiments describedherein.

The term “about” refers to the range of values approximately near thegiven value in order to account for typical tolerance levels,measurement precision, or other variability of the embodiments describedherein.

The terms “conductive,” “conductor,” “conductivity,” and the like referto the intrinsic ability of a material to facilitate electron or iontransport and the process of doing the same. The terms include materialswhose ability to conduct electricity may be less than typically suitablefor conventional electronics applications but still greater than anelectrically-insulating material.

The term “active material” and the like refers to the material in anelectrode, particularly in a cathode, that donates, liberates, orotherwise supplies the conductive species during an electrochemicalreaction in an electrochemical cell.

The term “transition metal” refers to a chemical element in groups 3through 12 of the periodic table, including scandium (Sc), titanium(Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr),niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium(Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum(Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum(Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium (Db),seaborgium (Sg), bohrium (Bh), hassium (Hs), and meitnerium (Mt).

The term “halogen” refers to any of the chemical elements in group 17 ofthe periodic table, including fluorine (F), chlorine (Cl), bromine (Br),iodine (I), and astatine (At).

The term “chalcogen” refers to any of chemical elements in group 16 ofthe periodic table, including oxygen (O), sulfur (S), selenium (Se),tellurium (Te), and polonium (Po).

The term “alkali metal” refers to any of the chemical elements in group1 of the periodic table, including lithium (Li), sodium (Na), potassium(K), rubidium (Rb), cesium (Cs), and francium (Fr).

The term “alkaline earth metals” refers to any of the chemical elementsin group 2 of the periodic table, including beryllium (Be), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

The term “rare earth element” refers to scandium (Sc), yttrium (Y),lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd),promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu).

A rate “C” refers to either (depending on context) the discharge currentas a fraction or multiple relative to a “1 C” current value under whicha battery (in a substantially fully charged state) would substantiallyfully discharge in one hour, or the charge current as a fraction ormultiple relative to a “1 C” current value under which the battery (in asubstantially fully discharged state) would substantially fully chargein one hour.

In certain embodiments, a novel active material is prepared for use in acathode with metal fluoride (MeF_(x)) active materials. In someembodiments, the novel active material, sometimes referred to herein asa hybrid material, is prepared by combining a metal fluoride and a metalcomplex, followed by heat treatment of the mixture under an inertatmosphere according to the Formula (I)

MeF_(x)+Me′_(y)X_(z)+heat  (I)

According to certain embodiments, the heat treatment of the metalfluoride and metal complex causes a reaction to form a new phaseaccording to the formula (II)

MeF_(x)+Me′_(y)X_(z)→Me_(a)Me′_(b)X_(c)F_(d)  (II)

where x, y, z, a, b, and c depend on the identity and valence of the Me,Me′, and X. In some instances, 0<a≦1, O<b≦1, 0≦c≦1, and 0≦d≦1. In otherembodiments, the heat treatment causes the formation of covalent bondsbetween the metal fluoride and the metal complex, improving conductivityand passivating the surface.

Suitable metal complexes, which can act as precursors for the reactiondescribed herein, for use in synthesizing the active material include,but are not limited to, MoO₃, MoO₂, NiO, CuO, VO₂, V₂O₅, TiO₂, A₁₂O₃,SiO₂, LiFePO₄, LiMe_(T)PO₄ (where Me_(T) is one or more transitionmetal(s)), metal phosphates, and combinations thereof. According toembodiments of the invention, these oxides can be used in Formula (I).

It is understood that the synthetic route for achieving the activematerial may vary, and other such synthetic routes are within the scopeof the disclosure. The material can be represented byMe_(a)Me′_(b)X_(c)F and in the examples herein is embodied by a Cu₃Mo₂O₉active material. Other active materials are within the scope of thisdisclosure, for example, NiCuO₂, Ni₂CuO₃, and Cu₃TiO₄.

The coating materials disclosed herein provide rechargeability tootherwise non-rechargeable metal fluoride materials. Without being boundby a particular theory or mechanism of action, the rechargeability maybe due to the electrochemical properties of the novel hybrid material,the coating of the metal fluoride to prevent copper dissolution, or amore intimate interface between the metal fluoride and the coatingmaterial as a result of the heat treatment and reaction. Further, thenovel hybrid material may provide a kinetic barrier to the Cudissolution reaction, or to similar dissolution reactions for othermetal fluoride materials to the extent such dissolution reactions occurin the cycling of electrochemical cells.

In the case of oxide-based hybrid materials, intimate mixing of themetal fluoride and the metal complex (or other suitable precursormaterial) and moderate heat treatment can be used to generaterechargeable electrode materials. Suitable coating precursors includematerials that decompose to form metal oxides (and in particular,transition metal oxides) as opposed to using a metal oxide to directlyreact with the metal fluoride. Examples of such precursors include, butare not limited to, metal acetates, metal acetylacetonates, metalhydroxides, metal ethoxides, and other similar organo-metal complexes.In either event, the final rechargeable material is not necessarily apure oxide or a purely crystalline material. The reaction of Formula IIpredicts that there would not be a pure oxide or a purely crystallinematerial. In some instances, the metal oxide precursor or metal oxidematerial can form a coating, or at least a partial coating, on the metalfluoride active material. Without being bound by a particular theory ormechanism of action, the reaction of the metal oxide precursor or metaloxide material with the surface of the metal fluoride (and in particularcopper fluoride) active material is important for generating arechargeable electrode active material.

EXAMPLES

The following examples describe specific aspects of some embodiments ofthe invention to illustrate and provide a description for those ofordinary skill in the art. The examples should not be construed aslimiting the invention, as the examples merely provide specificmethodology useful in understanding and practicing some embodiments ofthe invention.

Example 1 Fabrication of Hybrid and/or Coated Electrodes forRechargeable Cells

Materials and Synthetic Methods.

All reactions were prepared in a high purity argon filled glove box(M-Braun, O₂ and humidity contents<0.1 ppm). Unless otherwise specified,materials were obtained from commercial sources (e.g., Sigma-Aldrich,Advanced Research Chemicals Inc., Alfa Aesar, Strem) without furtherpurification.

Preparation of CuF₂ Hybrid.

Milling vessels were loaded with CuF₂ at from about 85 wt % to about 95wt % and reactant (metal oxide or metal oxide precursor) at from about 5wt % to about 15 wt %, and the vessels were sealed. The mixture wasmilled. After milling, samples were annealed at from about 200 degrees Cto about 575 degrees C for 1 to 12 hours under flowing N₂. Specifichybrid-forming reactants were processed as described below.

Preparation of CuF₂/Cu₃Mo₂O₉.

Milling vessels were loaded with CuF₂ (85 wt %) and MoO₃ (15 wt %),sealed, and then milled. After milling, samples were annealed at 450degrees C for 6 hours under flowing N₂.

Preparation of CuF₂/NiO.

Milling vessels were loaded with CuF₂ (85 wt %) and NiO (15 wt %),sealed, and then milled. After milling, samples were annealed at 325degrees C for 6 hours under flowing N₂.

Preparation of CuF₂Nickel(II) acetylacetonate.

A fine dispersion of CuF₂ was prepared by milling in the presence of THF(40-120 mg CuF₂/mL THF). The dispersed sample was then added to asolution of Ni(AcAc)2 in THF such that Nickel(II) acetylacetonateaccounted for 15 wt % of the solids in the solution. The solution wasthen agitated by either shaking, sonication, or low energy milling forfrom about 1 to about 12 hours. The solution was then dried at roomtemperature under vacuum and the resulting solid was annealed at 450degrees C for 6 hours under dry air.

Preparation of Vapor Deposited Coatings

The coating material (nickel metal) was vaporized and then physicallycondensed onto the substrate at 20 weight percent. X-ray diffractionmeasurements were performed on the coated material to confirm the bulkCuF₂ was not altered. The coated material was then annealed similarly tomaterials prepared by other methods.

Preparation of Atomic Layer Deposited Coatings

CuF₂ was coated with TiO₂ by atomic layer deposition methods. Theexpected coating thickness was about 8.5 nm based on ellipsometrymeasurements on a silicon witness sample, which represented a nominal 3weight percent coating on the CuF₂. The coated material was thenannealed similarly to materials prepared by other methods.

Electrode Formulation.

Cathodes were prepared using a formulation composition of 80:15:5(active material:binder:conductive additive) according to the followingformulation method: 133 mg PVDF (Sigma Aldrich) and about 44 mg Super PLi (Timcal) was dissolved in 10 mL NMP (Sigma Aldrich) overnight. 70 mgof coated composite powder was added to 1 mL of this solution andstirred overnight. Films were cast by dropping about 70 μL of slurryonto stainless steel current collectors and drying at 150 degrees C forabout 1 hour. Dried films were allowed to cool, and were then pressed at1 ton/cm². Electrodes were further dried at 150 degrees C under vacuumfor 12 hours before being brought into a glove box for battery assembly.

Example 2 Electrochemical Characterization of Electrochemical CellsContaining Rechargeable Electrodes

All batteries were assembled in a high purity argon filled glove box(M-Braun, O₂ and humidity contents<0.1 ppm), unless otherwise specified.Cells were made using lithium as an anode, Celgard 2400 separator, and90 μL of 1M LiPF₆ in 1:2 EC:EMC electrolyte. Electrodes and cells wereelectrochemically characterized at 30 degrees C with a constant currentC/50 charge and discharge rate between 4.0 V and 2.0 V. A 3 hourconstant voltage step was used at the end of each charge. In someinstances, cathodes were lithiated pressing lithium foil to theelectrode in the presence of electrolyte (1M LiPF₆ in 1:2 EC:EMC) forabout 15 minutes. The electrode was then rinsed with EMC and built intocells as described above, except graphite was used as the anode ratherthan lithium.

FIG. 1 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, the second cycledischarge capacity of three different cathode formulations containing aLiFePO₄ material is plotted as a function of LiFePO₄ content (labeledLFP) in the cathode in FIG. 1. The dotted line depicts the theoreticalcapacity of LiFePO₄. One cathode formulation is 100% LiFePO₄. Anothercathode formulation is a combination of CuF₂ and LiFePO₄ in which thecontent of LiFePO₄ was varied from 10% to 50% of the total weight ofconductive material. The third cathode formulation is a combination ofCuF₂ and the conventional conductive oxide MoO₃ and LiFePO₄ in which thecontent of LiFePO₄ was varied from 10% to 50% of the total weight ofconductive material. As this is second cycle data, FIG. 1 demonstratesthat all of the CuF₂/LiFePO₄ matrices are rechargeable. In addition, the(CuF₂/MoO₃)/LiFePO₄ hybrid cathode containing 50% LiFePO₄ is also ableto recharge. FIG. 1 further demonstrates a direct relationship betweenthe capacity and the percent content of LiFePO₄.

FIG. 2 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, the voltage of ahybrid cathode is plotted against the capacity for the first and secondcycles. The dashed line indicates the expected theoretical capacity fromthe LiFePO₄ content in cathode. The cathode formulation is the CuF₂(70%)/LiFePO₄ (30%) hybrid cathode from FIG. 1. During the first cycle,very little discharge capacity is observed, indicating that the LiFePO₄material is not capable of accepting charge on this cycle. Without beingbound to a particular theory or mechanism of action, the LiFePO₄material may not accept charge as a result of defects introduced duringmilling. This data suggests that all of the capacity observed during thefirst and second cycles can be attributed solely to the CuF₂.

FIG. 3 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, the dischargecapacity for cells with a range of LiFePO₄ content is plotted as afunction of cycle for 10 cycles. The cathode formulation is CuF₂ withLiFePO₄ content ranging from 10% to 50% of the total weight ofconductive material. FIG. 4 demonstrates that the hybrid cathode is ableto consistently recharge across a number of cycles. Based on data fromFIG. 2, it is expected that the discharge capacity is contributed solelyby CuF₂ and not LiFePO₄. This is a significant finding because CuF₂ hasnot been previously shown to have such significant reversible capacity.The combination of certain conductive materials with CuF₂ renders theCuF₂ cathode material rechargeable.

FIG. 4 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, the first and secondcycle voltage traces for a cell containing a cathode formed from a metalfluoride and the new hybrid material. In this case, the metal fluorideactive material is CuF₂ and the hybrid material is Cu₃Mo₂O₉. FIG. 4demonstrates that the cell has about 140 mAh/g of reversible capacity.Previously known cathodes containing CuF₂ have not demonstrated suchsignificant reversible capacity.

FIG. 5 illustrates the results of structural characterization of certainembodiments disclosed herein. Specifically, the powder X-ray diffractionpattern of the material forming the cathode tested in FIG. 4 is shownalong with the powder X-ray diffraction patterns of CuF₂ and Cu₃Mo₂O₉.FIG. 5 demonstrates that the material contains phases rich in CuF₂ andphases rich in Cu₃Mo₂O₉. Thus, FIG. 5 demonstrates a new hybrid materialin combination with a metal fluoride active material. Further, grainsize analysis of this powder X-ray diffraction data shows that the CuF₂has a grain size greater than 130 nm. This is a significant findingsince such comparatively large particles were thought to be too large toprovide good electrochemical performance.

For many of the rechargeable matrices described herein (and inparticular for matrices including Mo, Ni, or Ti), the reactionsdescribed herein yield a new material at least at the surface of theparticles of the metal fluoride active material. The novel materialpresent at least at the surface of the particles of the metal fluorideactive material is believed to provide many of the benefits disclosedherein.

FIG. 6 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, the second cycledischarge capacity of CuF₂ with various materials and annealingtemperatures. FIG. 6 shows many oxide materials that provide rechargecapability, demonstrated by capacities greater than 100 mAh/g.

Table 1 presents the results of further electrochemical characterizationof certain embodiments disclosed herein. Table 1 shows that many metaloxide and metal oxide precursor starting materials can be used in thereactions described herein to yield rechargeable metal fluorideelectrode materials. The materials in Table 1 include metal oxides,metal phosphates, metal fluorides, and precursors expected to decomposeto oxides. In particular, nickel oxide showed excellent performance.

TABLE 1 Electrochemical Characterization of Various Precursor Materialsas a Function of Anneal Temperature Initial Capacity ReversiblePrecursor Annealing Temp (0.02 C, Cy1, Capacity (0.05 C, Material (C.)mAh/g) Cy2, mAh/g) None 200 181 30 None 325 394 216 None 450 247 61(NH₄)H₂PO₄ 200 307 5 (NH₄)H₂PO₄ 325 406 178 (NH₄)H₂PO₄ 450 397 0 Al₂O₃200 281 70 Al₂O₃ 325 348 107 Al₂O₃ 400 203 78 AlF₃ 200 397 124 AlF₃ 325384 125 AlF₃ 400 320 98 AlPO₄ 200 410 115 AlPO₄ 325 356 136 AlPO₄ 450284 74 Bi₂O₃ 200 128 32 Bi₂O₃ 325 89 34 Bi₂O₃ 400 103 36 CaF₂ 200 301 86CaF₂ 325 310 107 CaF₂ 400 282 125 CaO 200 1 1 CaO 325 138 27 CaO 400 8429 Co₃(PO₄)₂ 200 323 93 Co₃(PO₄)₂ 325 373 161 Co₃(PO₄)₂ 450 382 126Co₃O₄ 200 167 112 Co₃O₄ 325 216 132 Co₃O₄ 450 329 151 Co₃O₄ 575 310 134Cr₂O₃ 200 223 88 Cr₂O₃ 325 234 132 Cr₂O₃ 450 227 102 Cr₂O₃ 575 184 70 FeAcetate 200 407 31 Fe Acetate 325 431 11 Fe Acetate 450 393 180 Fe₂O₃200 197 135 Fe₂O₃ 325 200 142 Fe₂O₃ 450 170 112 Fe₂O₃ 575 308 131 FeF₂200 427 202 FeF₂ 325 382 220 FeF₂ 400 370 155 FeF₃ 200 443 188 FeF₃ 325406 218 FeF₃ 400 359 141 FePO₄ 200 252 76 FePO₄ 325 393 147 FePO₄ 450429 197 In₂O₃ 200 250 64 In₂O₃ 325 203 106 In₂O₃ 400 347 109 La₂O₃ 200281 74 La₂O₃ 325 155 39 La₂O₃ 450 68 29 La₂O₃ 575 114 36 Li₂O 200 32 11Li₂O 325 49 18 Li₂O 400 38 18 Li₃PO₄ 200 318 123 Li₃PO₄ 325 435 136Li₃PO₄ 450 409 114 LiCoPO₄ 200 372 97 LiCoPO₄ 325 408 142 LiCoPO₄ 450338 136 LiH₂PO₄ 200 300 111 LiH₂PO₄ 325 423 149 LiH₂PO₄ 450 387 107LiMnPO₄ 200 351 77 LiMnPO₄ 325 368 102 LiMnPO₄ 450 397 178 LiNiPO₄ 200402 116 LiNiPO₄ 325 396 191 LiNiPO₄ 450 405 176 MgF₂ 200 387 135 MgF₂325 378 147 MgF₂ 400 360 122 MgO 200 313 181 MgO 325 259 155 MgO 400 198126 MnO 200 117 52 MnO 325 130 65 MnO 450 83 55 MnO 575 59 38 MnO₂ 200120 76 MnO₂ 325 123 57 MnO₂ 450 242 150 MnO₂ 575 104 69 Mo Acetate 200396 10 Mo Acetate 325 433 17 Mo Acetate 450 398 46 Na₂O 200 2 1 Na₂O 32526 13 Na₂O 400 24 13 Ni 200 345 197 Ni 325 301 178 Ni 400 302 158 Ni 450300 152 Ni acac 200 425 56 Ni acac 325 306 87 Ni Acac 400 247 30 Ni acac450 362 172 Ni acetate 200 397 148 Ni acetate 325 376 46 Ni acetate 350370 191 Ni acetate 400 383 180 Ni acetate 450 371 186 Ni acetate 500 373171 Ni₃(PO₄)₂ 200 410 124 Ni₃(PO₄)₂ 325 430 52 Ni₃(PO₄)₂ 450 126 44Ni(C₂O₂) 200 359 90 Ni(C₂O₂) 325 395 195 Ni(C₂O₂) 450 381 175 Ni(CP)₂200 304 27 Ni(CP)₂ 325 317 14 Ni(CP)₂ 450 258 148 Ni(OH)₂ 200 412 186Ni(OH)₂ 325 362 196 Ni(OH)₂ 400 327 181 Ni(OH)₂ 450 300 169 NiBr₂ 200125 0 NiBr₂ 325 225 78 NiBr₂ 400 244 113 NiCO₃*Ni(OH)₂ 200 380 17NiCO₃*Ni(OH)₂ 325 359 215 NiCO₃*Ni(OH)₂ 450 317 184 NiF₂ 200 367 121NiF₂ 325 395 207 NiF₂ 400 411 170 NiF₂ 450 396 177 NiO 125 257 131 NiO200 403 222 NiO 225 384 212 NiO 250 385 221 NiO 275 370 229 NiO 300 335175 NiO 325 402 252 NiO 350 365 209 NiO 375 260 123 NiO 400 371 200 NiO425 361 186 NiO 450 386 183 NiO 500 308 150 NiO 575 319 112 Sb₂O₃ 200111 34 Sb₂O₃ 325 147 37 Sb₂O₃ 400 223 104 Sc₂O₃ 200 359 159 Sc₂O₃ 325293 159 Sc₂O₃ 400 84 33 Sc₂O₃ 450 150 68 Sc₂O₃ 575 55 17 ScF₃ 200 400178 ScF₃ 325 387 174 ScF₃ 400 243 100 SiO₂ 200 1 1 SiO₂ 325 114 28 SiO₂400 230 92 SnO₂ 200 210 48 SnO₂ 325 182 68 SnO₂ 400 133 65 SrO 200 15212 SrO 325 66 16 SrO 400 134 48 Ta₂O₅ 200 289 4 Ta₂O₅ 325 269 141 Ta₂O₅450 298 121 Ta₂O₅ 575 317 74 Ti(OEt)₄ 200 438 21 Ti(OEt)₄ 325 453 12Ti(OEt)₄ 450 353 5 TiO₂ 225 322 150 TiO₂ 250 309 169 TiO₂ 275 262 162TiO₂ 300 199 127 TiO₂ 325 322 173 TiO₂ 350 327 187 TiO₂ 375 120 77 TiO₂400 359 199 TiO₂ 425 345 194 TiO₂ 450 353 169 Y₂O₃ 200 353 130 Y₂O₃ 325279 104 Y₂O₃ 450 83 37 Y₂O₃ 575 80 30 ZnF₂ 200 438 206 ZnF₂ 325 372 191ZnF₂ 400 318 134 ZnO 200 210 95 ZnO 325 242 93 ZnO 400 194 44 ZnO 450205 99 ZnO 575 151 71 ZrO₂ 200 302 122 ZrO₂ 325 288 129

FIG. 7 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, the second cycledischarge capacity for cells containing a cathode formed from a metalfluoride and the precursor material treated at different temperatures.In this case, the metal fluoride active material is CuF₂ and theprecursor material is NiO. FIG. 7 shows a peak for cycle 2 capacity atabout 325 degrees C for NiO precursors, with nearly 250 mAh/g dischargecapacity.

FIG. 8 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting 85 wt % CuF₂ with 15 wt % of certain metal oxides(in this case NiO or TiO₂) at certain annealing temperatures. Themixtures were milled at high energy for about 20 hours. The annealtemperatures ranged from about 225 degrees C to about 450 degrees C andthe anneal time was 6 hours. The 325 degree C anneal temperature for theNiO starting material generated the best performance. The cells used aLi anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testingwas performed at a rate of 0.02 C and over a voltage range of 2.0 V to4.0 V.

FIG. 9 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting 85 wt % CuF₂ with 15 wt % of certain metal oxides(in this case NiO or TiO₂) for certain annealing times. The mixtureswere milled at high energy for about 20 hours. The anneal temperaturewas 325 degrees C and the anneal time was 1 hour, 6 hours, or 12 hours.The 6 hour anneal time yielded the best results for both the NiO andTiO₂ starting materials, and the NiO starting material generated betterperformance. The cells used a Li anode and an electrolyte containing 1MLiPF₆ in EC:EMC. The testing was performed at a rate of 0.02 C and overa voltage range of 2.0 V to 4.0 V.

FIG. 10 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting 85 wt %, 90 wt %, or 95 wt % CuF₂ with 5 wt %, 10wt %, 15 wt % of NiO. The mixtures were milled at high energy for about20 hours. The anneal temperature was 325 degrees C and the anneal timewas 6 hours. Using 10 wt % or 15 wt % of the NiO starting materialgenerated better performance. The cells used a Li anode and anelectrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed ata rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.

FIG. 11 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The mixtureswere milled at various energies comparable to milling on a FritchPulverisette 7 Planatery Mill at 305, 445, 595, and 705 RPM for about 20hours. The anneal temperature was 325 degrees C and the anneal time was6 hours. Performance improves with increasing milling energy, suggestingthat intimate physical interaction of the materials is required. Thecells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC.The testing was performed at a rate of 0.05 C and over a voltage rangeof 2.0 V to 4.0 V.

FIG. 12 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The mixtureswere milled for various times (3 hours, 20 hours, or 40 hours) at a highenergy (comparable to 705 RPM on Fritch Pulverisette 7). The annealtemperature was 325 degrees C and the anneal time was 6 hours.Performance does not improve after 20 hours of milling. The cells used aLi anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testingwas performed at a rate of 0.05 C and over a voltage range of 2.0 V to4.0 V.

FIG. 13 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein. Specifically, FIG. 13 shows thesecond cycle reversible capacity measured for various starting materialsused to react with CuF₂. The starting materials include NiO, nickel(II)acetylacetonate (Ni acac in Table 1), nickel acetate, nickel hydroxide,NiCO₃*Ni(OH)₂, Ni(C₂O₂), Ni(CP)₂, and Ni. In some instances, thestarting materials react to form a new phase. The materials react withthe surface of the CuF₂ particles. Additionally, the anneal atmospherewas either N₂ or dry air. The precursor starting materials decompose toNiO (although this depends on the atmosphere for some precursors) at orbelow the annealing temperatures used for the reaction. The precursorsthat are soluble or have low boiling points can enable solution or vapordeposition processing methods. The cells used a Li anode and anelectrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed ata rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V. Severalmaterials show similar performance to the NiO baseline.

FIG. 14 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting CuF₂ with nickel(II) acetylacetonate using variousprocessing conditions. In some cases, the CuF₂ was dispersed usingmethods described herein. The coatings were applied using mill coatingtechniques (that is, agitating the mixture in a milling apparatus) or bysolution coating techniques (including solution coating driven byphysisorption). All samples were annealed under dry air. The cells useda Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testingwas performed at a rate of 0.05 C and over a voltage range of 2.0 V to4.0 V. Testing demonstrates that solution coating methods can providesimilar performance to the mill coating techniques.

FIG. 20 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the second-cyclecapacity retention and reversible capacity for cathode active materialsformed from reacting CuF₂ with coatings formed from various coatingmethods and from various precursors. The precursors included NiO, Ni,TiO₂, nickel(II) acetylacetonate, and nickel acetate. All five precursortypes were applied according to the mill coating techniques (that is,agitating the mixture in a milling apparatus). Solution coatingtechniques were used for nickel(II) acetylacetonate, and nickel acetate.Physical vapor deposition (PVD) techniques were used to form a coatingfrom Ni precursor, and atomic layer deposition (ALD) techniques wereused to form a coating from TiO₂. All samples were annealed under dryair. The cells used a Li anode and an electrolyte containing 1M LiPF₆ inEC:EMC. The testing was performed at a rate of 0.05 C and over a voltagerange of 2.0 V to 4.0 V.

The solution, vapor, and atomic layer deposition methods can providecomparatively more uniform coatings on metal fluoride particles than thecoatings obtained by milling methods. A comparatively thinner, moreuniform coatings can provide the benefits of the coating material, suchas more complete protection of the metal fluoride particle, with lessprecursor material. To the extent that excess precursor material is lessactive (and therefore less desirable) than the active material, thin,conformal coatings can provide an advantage in terms ofweight-normalized reversible capacity.

FIG. 20 shows that although absolute reversible capacity was inferiorfor solution and vapor coatings as compared to milled coatings, thereversible capacity per weight percentage of coating was significantlyimproved. For example, for the TiO₂ the atomic layer deposition coatingmethod yielded greater than about 60% more reversible capacity percoating weight than the milled coating method. The ALD coated materialhad a coating that was about 8 nm thick and less than about 3 weightpercent of the coated particle.

Notably, the non-milling coating methods shown in FIG. 20 (that is, thesolution coating, vapor deposition, and atomic layer deposition methods)are compatible with a subset of the metal complexes disclosed herein. Avariety of coating materials is possible with atomic layer depositionmethods including metals (e.g., Ni), metal oxides (e.g., A₁₂O₃, SiO₂,Ta₂O₅, TiO₂), metal nitrides (e.g., AlN, TaN), and others. Physicalvapor deposition techniques can also deposit coatings of a wide numberof materials including metals (e.g., Ni, Ba, Ta), metal oxides (e.g.,SiO₂, Ta₂O₅, TiO₂, NiO), metal nitrides (e.g., TiN, AlN), metalsilicates (e.g., ZrSiO₄) or other materials that are volatile enough tobe evaporated and re-condensed onto a substrate.

FIG. 15 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the capacity as afunction of cycle for cathode active materials formed from reacting 85wt %, CuF₂ with 15 wt % of NiO and for a control material. The NiO/CuF₂mixture was milled at high energy for about 20 hours. The annealtemperature was 325 degrees C and the anneal time was 6 hours. The cellsused a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. Thetesting was performed at a cycle 1 rate of 0.02 C, a cycle 2 rate of0.05 C, and a cycle 3 through cycle 25 rate of 0.5 C and over a voltagerange of 2.0 V to 4.0 V. With the reacted NiO/CuF₂ as the activematerial, the cell cycles reversibly for extended cycling with capacitygreater than 100 mAh/g for 25 cycles. Further, the reacted NiO/CuF₂active material demonstrates retention of 80% of cycle 3 capacity as farout as cycle 15. The control material, which was prepared according tothe process described in Badway, F. et al., Chem. Mater., 2007, 19,4129, does not demonstrate any rechargeable capacity. Thus, the materialprepared according to embodiments described herein is significantlysuperior to known materials processed according to known methods.

FIG. 16 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, a galvanostaticintermittent titration technique (GITT) measurement for cathode activematerials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO and fora control material. The NiO/CuF₂ mixture was milled at high energy forabout 20 hours. The anneal temperature was 325 degrees C and the annealtime was 6 hours. The cells used a Li anode and an electrolytecontaining 1M LiPF₆ in EC:EMC. The testing was performed over a voltagerange of 2.0 V to 4.0 V at a rate of 0.1 C and with a 10 hour relaxationtime. The GITT measurement relaxation points show low voltage hysteresis(about 100 mV), which indicate that the overpotential and/orunderpotential are likely caused by kinetic and not thermodynamiclimitations. This is consistent with other properties andcharacteristics observed for the reacted NiO/CuF₂ active material.

FIG. 17 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the capacity of fullcells and half cells as a function of cycle for cathode active materialsformed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The NiO/CuF₂mixture was milled at high energy for about 20 hours. The annealtemperature was 325 degrees C and the anneal time was 6 hours. The label“Cu+2LiF” indicated that the NiO/CuF₂ electrode was lithiated bypressing Li foil to CuF2 electrode in the presence of electrolyte asdescribed above. The other half cell was lithiated electrochemically inthe initial cycles. The cells used a Li anode and an electrolytecontaining 1M LiPF₆ in EC:EMC. The testing was performed over a voltagerange of 2.0 V to 4.0 V. Half cell performance is essentially identicalbetween the two lithiation methods after cycle 2, while full cell showsadditional irreversible capacity loss as compared to the half cells butsimilar capacity retention.

FIG. 18 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the voltage tracesof the full cell and half cells prepared as described in relation toFIG. 17. The full cell has similar charge capacity to the half cells,but larger irreversible capacity loss and lower discharge voltage (whichcan indicate increased cell impedance). FIG. 18 demonstrates that thefull cell has about 250 mAh/g of reversible capacity and about 500 mVhysteresis between charge and discharge plateau voltages.

FIG. 19 illustrates the results of electrochemical characterization ofcertain embodiments disclosed herein, specifically, the capacityretention of full cells and half cells as a function of cycle forcathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt %of NiO. The results from a control material are also depicted. The fullcell and half cells were prepared as described in relation to FIG. 17.The cells used a Li anode and an electrolyte containing 1M LiPF₆ inEC:EMC. The testing was performed at a cycle 1 rate of 0.1 C and over avoltage range of 2.0 V to 4.0 V. The capacity retention is essentiallyidentical for the full and half cells of the NiO/CuF₂ active material.The control material shows essentially no rechargeable capacity.

While the invention has been described with reference to the specificembodiments thereof, it should be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the true spirit and scope of the invention asdefined by the appended claims. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,method, or process to the objective, spirit and scope of the invention.All such modifications are intended to be within the scope of the claimsappended hereto. In particular, while the methods disclosed herein havebeen described with reference to particular operations performed in aparticular order, it will be understood that these operations may becombined, sub-divided, or re-ordered to form an equivalent methodwithout departing from the teachings of the invention. Accordingly,unless specifically indicated herein, the order and grouping of theoperations are not limitations of the invention.

We claim:
 1. A method of making an electrode, comprising: coatingparticles, wherein each particle includes a metal fluoride material,with a coating precursor material, wherein the coating precursormaterial includes a transition metal; annealing the particles such thatat least a portion of the metal fluoride material and at least a portionof the transition metal react to undergo a phase change; and forming thecoated particles into an electrode.
 2. The method of claim 1, whereinthe electrode forming step comprises preparing a formulation compositionof coated particles, binder, and conductive additive.
 3. The method ofclaim 1, wherein the metal fluoride material comprises copper fluoride.4. The method of claim 1, wherein the coating step comprising millingthe particles with the coating precursor material.
 5. The method ofclaim 4, wherein the coating precursor material comprises a organo-metalcomplex.
 6. The method of claim 4, wherein the coating precursormaterial comprises a metal oxide.
 7. The method of claim 4, wherein thecoating precursor material comprises elemental metal.
 8. The method ofclaim 4, wherein the coating precursor material comprises NiO.
 9. Themethod of claim 4, wherein the coating precursor material comprisesTiO₂.
 10. The method of claim 4, wherein the coating precursor materialis Ni.
 11. The method of claim 4, wherein the coating precursor materialcomprises nickel(II) acetylacetonate.
 12. The method of claim 4, whereinthe coating precursor material comprises nickel acetate.
 13. The methodof claim 1, wherein the coating step comprises a solution coatingprocess.
 14. The method of claim 13, wherein the coating precursormaterial comprises an organo-metal complex.
 15. The method of claim 13,wherein the coating precursor material comprises nickel(II)acetylacetonate.
 16. The method of claim 1, wherein the coating stepcomprises a physical vapor deposition process.
 17. The method of claim16, wherein the coating precursor material comprises a metal oxide. 18.The method of claim 16, wherein the coating precursor material comprisesa metal nitride.
 19. The method of claim 16, wherein the coatingprecursor material comprises a metal silicate.
 20. The method of claim16, wherein the coating precursor material is Ni or Ti.
 21. The methodof claim 1, wherein the coating step comprises an atomic layerdeposition process.
 22. The method of claim 21, wherein the coatingprecursor material is Ni.
 23. The method of claim 21, wherein thecoating precursor material comprises a metal oxide.
 24. The method ofclaim 21, wherein the coating precursor material comprises a metalnitride.
 25. The method of claim 1, wherein the annealing step isconducted at a temperature less than or equal to 450 degrees C.
 26. Themethod of claim 1, wherein the annealing step is conducted at atemperature less than or equal to 325 degrees C.
 27. An electrode formedby the method of claim
 1. 28. The electrode of claim 27 wherein theelectrode is characterized by having reversible capacity.
 29. Theelectrode of claim 27 comprising particles having a first phase and acoating on the particle having a second phase.
 30. The electrode ofclaim 29 wherein the coating is covalently bonded to the particle